1. Field of the Invention:
The present invention relates to an automatic locking retractor for a seat belt assembly used, for example, in motor-vehicles. More particularly, the present invention relates to an automatic locking retractor provided with an improved locking mechanism which makes it impossible to pull out a webbing beyond a certain length by first pulling out the webbing in excess and retracting it slightly for a buckling operation, thereby to secure seat occupants and to prevent injury or physiological damage caused by any traffic accident.
2. Description of the Prior Art:
In recent years, the majority of automobiles are provided with seat belts in accordance with safety regulations now enforced almost throughout the world for the purpose of protecting seat occupants against any unexpected traffic accident. In addition to buckle assemblies necessary for such seat belts, various kinds of retractors have been proposed for the seat belts. Among the retractors now put in practice, those of an automatically locking type, i.e. automatic locking retractors (ALR), are widely known. The retractors of this type now proposed have various structures but are constructed basically by a shaft for pulling out or rewinding a webbing, a lock mechanism for the shaft and a control means for the lock mechanism. Typical examples of the conventional automatic locking retractors are disclosed in Japanese Laid-open Utility Model Applns. Nos. Sho. 60-11858 and Sho. 60-55565 (U.S. Pat. No. 4,585,186). The automatic locking retractor for a seat belt disclosed in Japanese Laid-open Utility Model Appln. No. Sho. 60-11858 comprises, as shown in FIGS. 1-6, a takeup shaft 22A for a webbing 24, a rachet wheel 28 being rotatable coaxially with the takeup shaft, a pawl 30 capable of taking a locked position or an unlocked position to the rachet wheel 28, a diameter-sensing means 34 capable of sensing the diameter fo the roll of webbing wound on the takeup shaft to let the pawl take the locked position to the rachet wheel only in the case of the roll being smaller than a predetermined amount and a spring member (control member) having on both ends thereof a first leg and a second leg each extending from the outer periphery of the rachet, the spring member 36 being fitted on the shaft in such a manner that the member 50 is slidable with friction on the shaft and rotatable within a restricted range defined by a pair of pins 42 and 44 mounted to the rachet wheel 28.
In case the seat belt is not used, the webbing is kept fully wound on the rotatable takeup shaft whereby the pawl is located in an unlocked position to the rachet wheel by means of the diameter-sensing means. When the webbing is pulled out, the shaft is rotated in the direction of the webbing being pulled out and the spring member is incidentally rotated within a predetermined range in the same direction. In this state, the spring member holds the pawl in the unlocked position to the rachet wheel in such manner that the first leg positioned in rear of the second leg in the direction of the webbing being pulled out supports the pawl. As the pawl is not engaged with the rachet wheel, the shaft can freely be rotated to pull out the webbing over a necessary length for a buckling operation. When the webbing pulled out in excess length is retracted after the buckling operation, the takeup shaft is rotated in the opposite direction (in the direction of the webbing being rewound) and the spring member is also rotated incidentally whereby the pawl is supported by the second leg in place of the first leg and is consecutively located in the unlocked position to the rachet wheel. If the body of the seat belt wearer is moved forward by a sudden braking or traffic accident, the webbing will be pulled out of the retractor to permit rotation of the shaft in the direction of pulling out the webbing whereby the spring member will be incidentally rotated with the result that the pawl will be detached from the second leg and engaged with the rachet wheel to take a locked position thereto, thus inhibiting the webbing from further being pulled out. Consequently, the seat belt is not loosened and keeps the wearer fastened to the seat in case of a sudden braking or traffic accident. When the seat belt wearer operates the buckle to unfasten the seat belt, the webbing is fully rewound on the takeup shaft which is energized at all times to rotate in the rewinding direction by resiliency of a spring means, whereby the pawl is supported by the second leg to take the unlocked position to the rachet wheel.
The automatic locking retractor disclosed in Japanese Laid-open Utility Model Appln. No. Sho. 60-55565 (U.S. Pat. No. 4,585,186) is similar in structure to that disclosed in the aforementioned Japanese Laid-open Utility Model Appln. No. Sho. 60-11858 but some modifications are made especially in the spring member 36 so as to form a hairpin-like projection in the central part instead of the two legs on both ends. The spring member 36 is rotatable with the rachet wheel 28 within a restricted range defined by two pins 42 and 44 (FIGS. 2 and 3) or one pin 45 (FIGS. 4 and 5) mounted to the rachet wheel and controls the engagement of a pawl 30 with the rachet wheel 28. Thus, this automatic locking retractor is somewhat simplified in structure but achieves basically an equivalent effect.
These prior art automatic locking retractors are seemingly provided with a satisfactory automatic locking mechanism but still have some detrimental drawbacks to be overcome in practical use. In the automatic locking retractor disclosed in Japanese Laid-open Utility Model Appln. No. Sho. 60-11858, the second leg 38 holds the pawl 30 in the unlocked position to the rachet wheel 28 under normal belt-wearing conditions. If the webbing 24 is strongly pulledy out in such a state, the takeup shaft 22A and the rachet wheel 28 will be rotated rapidly in the direction of the webbing being pulled out to swing the pawl 30 whereby some time lag may take place for the engagement with the rachet wheel. During such time lag, the first leg 40 located in rear of the second leg 38 in the direction of the webbing being pulled out is interposed between the pawl 30 and the rachet wheel 28 to hold the pawl in the unlocked position to the rachet wheel whereby the webbing is freely pulled out. In case of a sudden braking or any traffic accident, the body of the belt-wearer is moved forward by inertia whereby the webbing is strongly pulled out. Thus, the automatic locking mechanism of this retractor does not function completely in case of any accident whereby the belt-wearer is exposed to an unexpected dangerous conditions.
Another drawback found in this retractor is the so-called "automatic body-squeezing phenomenon" generally observed in the prior art antomatic locking retractors. The rachet wheel 28 has a number of teeth on the periphery thereof for engagement with the pawl 30. On the other hand, the webbing is at all times pulled in the rewinding direction as the takeup shaft 22A is energized to rotate in the rewinding direction by a spring means. When the body of the belt-wearer is swung during driving of the motor-vehicle, the webbing is also swung and may sometimes be pulled out. In this case, the pawl is allowed to engage with the rachet wheel to prevent the webbing from being pulled out further. Since the rachet wheel 28 is at all times energized to rotate together with the takeup shaft 22A in the direction of the webbing being rewound and since the interval between the teeth (i.e. the distance to the adjacent tooth) on the periphery of the rachet wheel 28 is relatively short, the pawl located in a certain tooth of the rachet wheel tends to move to the adjacent tooth in accordance with the rewinding force acting on the webbing, while keeping the engagement with the rachet wheel, whenever the body of the belt-wearer is swung. If this tendency is strong, the body of the belt-wearer will gradually be squeezed tightly, causing an unpleasant feeling for the belt-wearer.
In the automatic locking retractor disclosed in Japanese Laid-open Utility Model Appln. No. Sho. 60-55565 (U.S. Pat. No. 4,585,186), the first mentioned drawback as seen in the case of any traffic accident with respect to the retractor disclosed in Japanese Laid-open Utility Model Appln. No. Sho. 60-11858 is overcome to a certain degree, but the second mentioned drawback based on the "automatic body-squeezing phenomenon" is not overcome at all.
In addition to the above drawbacks, these prior art automatic locking retractors have a common problem in that an unpleasant click noise occurs when the webbing is rewound. This is due to the fact that the pawl is allowed to abut against a number of teeth formed on the periphery of the rachet wheel upon rewinding the webbing.
In view of the foregoing situations, further improvements are required in the prior art automatic locking retractors as disclosed in the aforesaid publications to overcome all the drawbacks mentioned above thereby achieving assured operation of the locking mechanism and removing unpleasant feeling during use. In the practical aspect, therefore, there is a great demand for developing a new type of automatic locking retractor for a seat belt assembly, which is improved in its automatic locking mechanism for assured operation and satisfactorily overcomes the drawbacks seen in the prior art similar retractors.